A study will be made of the physical, chemical, and biochemical mechanisms of interactions between proteolytic enzymes and naturally occurring protein inhibitors of proteolytic enzyme. Inhibitors and enzymes of differing physical and chemical properties and different specificities will be used. The enzymes will include; trypsin, alpha- chymotrypsin, kallikrein, subtilisin, and elastase. The inhibitors will include: avian ovomucoids, avian ovoinhibitors, lima bean inhibitor, and Kunitz pancreatic inhibitor. The interactions will be characterized by physical and chemical methods including ultracentrifugation, gel electrophoresis and filtration, spin and nuclear magnetic labelling, and other similar methods. Chemical modification of the structures of the enzymes and the inhibitors will be a primary tool.